1. Field of the Invention
This invention relates to polymeric colorants, particularly water-soluble polymeric black colorants useful as water-based printing ink components.
2. The Prior Art
An ideal black dye exhibits a strong absorbance throughout the visible color range. There are two basic ways to achieve this. The first is to intentionally or inadvertently combine a number of colors which separately absorb various portions of the color range. Nigrosine, a widely accepted black dye, is such a mixture. This method has an advantage that color shading is simply accomplished by varying the mixture's composition and the disadvantage of separating into its components under certain conditions.
The second type of black dye employs a single chromophore having a very broad absorbance. This is easily done with insoluble "carbon black" type materials but far more difficult to attain with soluble systems. The present invention relates to such a "single dye" soluble system.
The colorant of this invention is a polymeric colorant. Polymeric colors are known to offer advantages in use of noncorrosivity (U.S. Pat. No. 3,976,797, issued Aug. 24, 1976) and nonmigration in substrates (U.S. Pat. No. 3,937,851, issued Feb. 10, 1976). In addition, they can be made water-soluble--an advantage today with increasing opposition to widespread use of organic solvented dye systems which release organic solvents into the workplace.
We and our coworkers have prepared and reported a number of polymeric colors heretofore. For example, U.S. Pat. No. 3,920,855, issued Nov. 18, 1975 discloses a family of nonabsorbable polymeric food colors. These materials employ known chromophores. U.S. Pat. No. 4,018,826, issued Apr. 19, 1977 discloses poly(vinylamine) as a colorant backbone and shows a range of polymeric colorants. U.S. Pat. Nos. 4,051,138, issued Sept. 27, 1977; 4,096,134, issued June 20, 1978; 4,182,885, issued Jan. 8, 1980; and 4,233,328, issued Nov. 11, 1980 are representative of other patents dealing with polymeric colorants. These references have either achieved polymeric forms of colors having hues that match those of their known monomeric equivalents or have employed newly discovered chromophore units. In contrast, the present colors employ a known chromophore unit (Acid Blue 92), but modify and couple it in a way that changes its color from a monomeric blue to a polymeric black.